Launch Weather:
A large high pressure system was centered over the southeastern US on launch day. Winds at the Kennedy Space Center (KSC) were east-northeast at the surface through three thousand feet and easterly above that through six thousand feet. A layer of scattered to broken low clouds was south of a line that extended from just south of KSC up to the northeast. The clouds at the Shuttle Landing Facility (SLF) at KSC were forecast to remain scattered. Peak winds occasionally exceeded the crosswind limit during the launch count. This was expected and had been briefed to the flight control team. The RTLS forecast verified with few clouds reported at five thousand feet and winds below the crosswind limit.

A broad upper-level trough covered the three Trans-oceanic Abort Landing sites. Strong and gusty winds just above the headwind limit were forecast at Zaragoza, Spain, and low cloud ceilings and showers were expected at Ben Guerir, Morocco. The gusty winds at Zaragoza verified just under the headwind limit and showers were reported around Ben Guerir. No weather flight rule violations were reported at Moron, Spain, as forecast.

Landing Weather:
Saturday, April 28th, four days before the rescheduled landing, SMG's forecast indicated the possibility of No-Go weather conditions at KSC at landing time. A large high pressure system over the Great Lakes was forecast to move southeast off the coast of Virginia by Tuesday as an upper-level disturbance over the northwestern Gulf of Mexico drifted east bringing crosswinds and showers to KSC on Tuesday.

By Monday, the day before landing, the upper-level disturbance had moved over the northern Gulf of Mexico and the high was centered on the Maryland coast. The high covered an area from northern Maine to southern Florida and was forecast to drift southeast overnight and become nearly stationary. The upper-level disturbance was expected to drift east, finally moving over Florida mid-week. Mission managers were briefed Monday morning that No-Go conditions due to showers, low ceilings, and crosswind violations were forecast for KSC through the week, Tuesday through Friday. Edwards Air Force Base, the alternate landing site, would be under the influence of a weak upper-level high and would have clear skies and light winds on Tuesday. However, gusty northeast winds were expected to develop Wednesday and continue Thursday as an upper-level trough developed over the western US and a surface high pushed into the Pacific Northwest. The managers decided to call up Edwards support for Tuesday based on wind variability at Edwards.

The entry team arrived late Monday night and issued the forecast issued early Tuesday morning. Both landing opportunities for KSC were forecast No-Go due to showers within 30 NM, ceilings, and crosswinds, all in violation of weather flight rules. Similar conditions were forecast for Wednesday and Thursday. Clear skies and light winds were forecast for Edwards on Tuesday. The models continued to indicate gusty northeast winds for Wednesday and stronger northeast winds for Thursday. There was some concern that the winds at Edwards might come out of the west rather than the northeast on Wednesday if the trough developed further west than expected or the high did not move as fast to the east. Westerly winds might exceed the crosswind limit. This was briefed to the entry Flight Director, the flight control team, and managers.

Showers, crosswinds, low ceilings, and occasionally low visibilities in showers were observed at KSC through the landing count. The Flight Director waved off the first KSC opportunity. Conditions at Edwards remained as expected with clear skies and light winds. A mission management team meeting was called to review the forecasts. Mission managers decided that with No-Go weather forecast for KSC tomorrow (Wednesday) they would be in favor of landing at Edwards today rather than waiting 24 hours and landing at Edwards tomorrow.

Clear skies and light winds continued at Edwards. After waving off the second KSC opportunity, the Flight Director made the decision to land on the first available opportunity at Edwards. The shuttle touched down on runway 22 at Edwards Air Force Base, California at 1611 UTC (11:11 AM CDT) under clear skies and light westerly winds.

SMG Lead Meteorologist Karl Silverman worked his 42nd mission, 7th as Lead. Richard Lafosse was Assistant Lead and TAL Forecaster and Tim Oram was the Techniques Development Unit Meteorologist.

More information on NASA's Space Shuttle and the International Space Station, as well as information about the Spaceflight Meteorology Group is available on the web.

Submitted by:
Karl A. Silverman
STS-100 Lead Meteorologist